How to Convert/add String Array[] elements into List<String> [] Array

I have three arrays of String

String array1 [] = {"A", "B", "C"};
String array2 [] = {"D", "E"};
String array3 [] = {"F", "G", "H", "I"};

I want to store all this arrays into List of String array.

List<String> allArrays[]

My output List<String> allArrays[] should contain

allArrays[0]= [A,B,C]
allArrays[1]= [D,E]
allArrays[2]= [F,G,H,I]

I have tried below piece of code but getting null pointer exception

String array1 [] = {"A", "B", "C"};
String array2 [] = {"D", "E"};
String array3 [] = {"F", "G", "H", "I"};

List<String> allArrays[] =null;

allArrays[0].addAll(Arrays.asList(array1));
//Null pointer exception here
allArrays[1].addAll(Arrays.asList(array2));
allArrays[2].addAll(Arrays.asList(array3));

System.out.println(b[0]);
System.out.println(b[1]);
System.out.println(b[2]);

You are not creating and adding to the list correctly. Since you need an array of List<String>, you can do this:

String array1 [] = {"A", "B", "C"};
String array2 [] = {"D", "E"};
String array3 [] = {"F", "G", "H", "I"};
List<String>[] allArrays = new ArrayList[3]; 

List<String> list = new ArrayList<String>();
Collections.addAll(list, array1);
allArrays[0] = list;
list = new ArrayList<String>();
Collections.addAll(list, array2);
allArrays[1] = list;
list = new ArrayList<String>();
Collections.addAll(list, array3);
allArrays[2] = list;
	    
System.out.println(allArrays[0]);
System.out.println(allArrays[1]);
System.out.println(allArrays[2]);

Output:

[A, B, C]
[D, E]
[F, G, H, I]

A better way would be using List<List<String>>:

String array1 [] = {"A", "B", "C"};
String array2 [] = {"D", "E"};
String array3 [] = {"F", "G", "H", "I"};
List<List<String>> allArrays = new ArrayList<>(); 

allArrays.add(Arrays.asList(array1));
allArrays.add(Arrays.asList(array2));
allArrays.add(Arrays.asList(array3));
		        
System.out.println(allArrays);

Output:

[[A, B, C], [D, E], [F, G, H, I]]

Try this:

String[] array1 = {"A", "B", "C"};
String[] array2 = {"D", "E"};
String[] array3 = {"F", "G", "H", "I"};

List<String>[] listArr = new ArrayList[3];
listArr[0] = new ArrayList<>(Arrays.asList(array1));
listArr[1] = new ArrayList<>(Arrays.asList(array2));
listArr[2] = new ArrayList<>(Arrays.asList(array3));

for (int i = 0; i < 3; i++) {
    System.out.println(listArr[i]);
}

Try this.

String array1 [] = {"A", "B", "C"};
String array2 [] = {"D", "E"};
String array3 [] = {"F", "G", "H", "I"};

List<String>[] allArrays = new List[] {
    Arrays.asList(array1),
    Arrays.asList(array2),
    Arrays.asList(array3)
};

System.out.println(Arrays.toString(allArrays));

output

[[A, B, C], [D, E], [F, G, H, I]]

Of course you get a null Pointer Exception, because you need to creat a new List. If you set your List to null, you dont create a empty List, you just have a Object, which you can do nothing with.

    String array1 [] = {"A", "B", "C"};
	String array2 [] = {"D", "E"};
	String array3 [] = {"F", "G", "H", "I"};

	List<String[]> allArrays;
	
	allArrays = new LinkedList<>();


	allArrays.add(array1); 
	allArrays.add(array1); 
	allArrays.add(array1); 
	
	String[] array4 = allArrays.get(0);
	String[] array5 = allArrays.get(1);
	String[] array6 = allArrays.get(2);

	System.out.println(array4);
	System.out.println(array5);
	System.out.println(array6);

It should work if you do it with a LinkedList. By the way, are you using a IDE, when I put your code in Eclipse or any other IDE I get many Warnings, so the NullPointerException wasnt the only that doesnt work in your code.